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      Question

      If the radius of a right circular cylinder open at both

      ends, is decreased by 25% and the height of the cylinder is increased by 20%, then the percentage change in curved surface area of the cylinder thus formed is.
      A 40%increased Correct Answer Incorrect Answer
      B 10%decreased Correct Answer Incorrect Answer
      C 10% increased. Correct Answer Incorrect Answer
      D 40%decreased Correct Answer Incorrect Answer

      Solution

      Let height of the cylinder and radius of the cylinder =100 Then surface area of the cylinder=2×3.14×100×100 =62800 Now- When 25%decreased in radius =100×75/100=75 And 20%increase in height=100×120/100=120 Now surface area of the cylinder=2×3.14×75×120=56520 Change in curved surface area=62800-56520= 6280 decresed %decreased=6280/62800×100 =10% decreased Trick- To [m + n+ (m × n) /100] =-25+(20) +(-25×20)/100 =-25+20-5 =-30+20 = -10% 

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